1. Field of the Invention
The present invention relates to an electrophotographic photoconductor containing a charge generation layer and a charge transport layer sequentially arranged and manufacturing process thereof, and to an electrophotographic apparatus and a process cartridge for electrophotographic apparatus containing the electrophotographic photoconductor. More specifically, it relates to an electrophotographic photoconductor that shows less variation in sensitivity and excellent electrostatic properties even when a halogen-free coating solvent is used, and to an image forming apparatus and a process cartridge for image forming apparatus containing the electrophotographic photoconductor.
2. Description of the Related Art
Information processing systems using electrophotographic process have been dramatically developed. Among them, optical printers convert information into digital signals, produce records on information optically and thereby have remarkably improved print quality and reliability. In addition to printers, the digital recording technique is also applied to regular copiers, to yield “digital” copiers. Copiers using the digital recording technique in addition to conventional analogue copying techniques can have a variety of information processing functions and are expected to be increasingly used. In addition, with an increasing proliferation and improved properties of personal computers, digital color printers for output of color images and documents have rapidly advanced.
Electrophotographic photoconductors utilizing organic photoconductive materials exhibiting outstanding properties in terms of sensitivity, thermal stability and toxicity as compared with conventional inorganic materials as Se, CdS, and ZnO are now widely used in such image forming apparatus. As a photoconductive layer of an electrophotographic photoconductor using the organic photoconductive material, one comprising a charge generation layer and a charge transport layer arranged sequentially and thus having separated functions in the individual layers is generally used for its excellent sensitivity and durability.
A variety of charge generation materials such as azo pigments, polycyclic quinone pigments, trigonal selenium and phthalocyanine pigments have been developed for use in the charge generation layer. Among them, phthalocyanine pigments show high sensitivity with respect to light with long wavelengths of 600 nm to 800 nm and are very important and useful as photoconductive materials for electrophotographic printers and digital copiers using a light-emitting diode (LED) or a laser diode (LD) as a light source.
The charge transport layer mainly contains a charge transport material and a binder resin and is generally prepared by dissolving or dispersing these materials in a solvent to form a coating composition, and applying the coating composition. A halogen-containing solvent such as dichloromethane or chloroform is generally used as the solvent for satisfactory solubility or dispersibility and coating ability.
With an increasing environmental aware, a demand has been made to develop photoconductors using halogen-free solvents that affect the human body and environment less. However, a photoconductor prepared using a coating composition for charge transport layer using a halogen-free solvent shows decreased optical sensitivity in initial stages and/or after repetitive use, although it has increased electrostatic properties.
As a possible solution to prevent such a decreased sensitivity, Japanese Patent Application Laid-Open (JP-A) No. 04-318557 (page 3, left column, lines 5-33 in Japanese) and Journal of Imaging Science, vol. 35, No. 4, p. 235 (1991) each disclose a method for increasing the optical sensitivity by milling a phthalocyanine pigment to thereby reduce its particle diameter.
JP-A No. 2001-115054 discloses a titanyl phthalocyanine containing unchlorinated titanyl phthalocyanine and a chlorinated titanyl phthalocyanine in a specific amount, and a titanyl phthalocyanine having an average particle diameter of 1 μm or less (Claims 1 and 3; and page 3, right column, lines 10-20 in Japanese).
However, when these techniques are applied to a photoconductor using a halogen-free solvent in a coating composition for charge transport layer, the optical sensitivity significantly decreases in the initial stage and/or after repetitive use.
JP-A No. 10-326023 discloses the use of a dioxolane compound as a halogen-free organic solvent (Claims 1; and page 3, left column, lines 15-21 in Japanese). JP-A No. 2001-356506 discloses a coating composition for charge transport layer containing a cyclic ether solvent such as tetrahydrofuran and, in addition, a specific stabilizer such as antioxidant or ultraviolet absorber, since such a cyclic ether solvent generates a peroxide after leaving stand (Claim 1; and page 5, right column, lines 41-45 in Japanese).
However, these techniques insufficiently solve the above problems or invite decreased sensitivity due to the additives.
Demands have therefore been made on an electrophotographic photoconductor showing satisfactory optical sensitivity in the initial stage and even after repetitive use and having outstanding electrostatic properties even when a halogen-free solvent is used in a coating composition for charge transport layer, as well as an image forming apparatus using the electrophotographic photoconductor, and a process cartridge for the image forming apparatus.